Using Log4Net's FileAppender in a web garden

Whilst you might not think you're running a web garden (that is: running your website in two or more processes simultaneously on the same machine), it's worth checking in case your server SOE catches you by surprise (hint: this happened to me):



Obviously in this scenario it's not just log4net you've got to watch out for, but anything you're saving on the local filesystem is a candidate for cross-process resource contention. In log4net's case, the RollingFileAppender can block itself (in the other process).

There's a couple of ways round this. You can configure the FileAppender to minimize the amount of time it locks the file (the MinimalLock attribute), but for diagnostic simplicity I prefer to configure each web application instance to log to a different file. Something like this:

 <appender name="File" type="log4net.Appender.RollingFileAppender">
  <file type="log4net.Util.PatternString" value="C:\temp\MyApp_[%processid].log" />
  <datePattern value="yyyyMMdd"/><!--roll the file daily-->
  <rollingStyle value="Date"/>
  <appendToFile value="true"/>
    
  <layout type="log4net.Layout.PatternLayout">
   <conversionPattern value="%date{ABSOLUTE} [%thread] %-5level %logger.%method() - %message [%identity]%newline" />
  </layout>
 </appender>

This way if anything screwy happens in one of the instances (it didn't start alltogether?) it's easier to isolate.

PS: Blogger is so not the right engine to be doing this XML stuff in...